1. Field of the Invention
The present invention relates to a barrel mounted to image-taking apparatus such as silver halide camera and digital still cameras, and more specifically video cameras, etc.
2. Description of the Related Art
FIG. 6 shows a barrel of a conventional camera (see Japanese Patent Application Laid-Open Publication No. H07(1995)-043584). In the figure, numeral 101 denotes a rectilinear barrel, and this rectilinear barrel 101 is positioned inside a differential barrel not illustrated. When this differential barrel moves in the optical axis direction while the differential barrel rotates around the optical axis, the rectilinear barrel 101 moves in the optical axis direction in linkage with the movement of the differential barrel while the rectilinear barrel 101 does not rotate around the optical axis.
To the rectilinear barrel 101, three guide groove portions 101d extending along the optical axis direction are located at nearly even intervals. To guide the groove portion 101d, a cam pin (not illustrated) mounted to a lens holding member to be assembled inside the rectilinear barrel 101 is engaged.
At the rear end portion of the rectilinear barrel 101, a flange portion 101a that extends along the circumferential direction of the rectilinear barrel 101 is positioned. At the position of the phase same as that of the guide groove portion 101d of the flange portion 101a, an opening 101c for passing the cam pin is provided. When a lens holding member is assembled to the rectilinear barrel 101, the cam pin can be guided to guide the groove portion 101d in such a manner as to pass the opening portion 101c from the rear side of the rectilinear barrel 101.
In addition, to the flange portion 101a, a protruded portion 101b is positioned at the location of the phase same as that of the opening portion 101c. This protruded portion 101b prevents the rectilinear barrel 101 from rotating around the optical-axis by engaging with a rectilinear groove portion formed in a fixed barrel (either not illustrated).
As described above, in the conventional lens barrel, the opening portion 101c and the protruded portion 101b are arranged at the position of the same phase. This is because strength is weakened at the place where the opening portion 101c of the flange portion 101a is formed because the size in the height direction of the flange portion is shortened. That is, the protruded portion 101b is arranged at the position of the phase same as that of the opening portion 101 and the strength of the flange portion 101a is prevented from being degraded.
However, if it is mandatory to arrange the protruded portion 101b at the position of the phase same as that of opening portion 101c, the degree of design freedom is impaired. That is, the protruded portion 101b must be arranged in such a manner as to engage with the rectilinear groove portion formed in the fixed barrel. Consequently, the opening portion 101c, the guide groove portion 101d, the protruded portion 101b, and the rectilinear groove portion of the fixed barrel must be arranged at the position of the same phase. This may impair the degree of design freedom.